Pedicle screw

ABSTRACT

A pedicle screw comprises a head. A shaft is joined to the head. The shaft comprises a first threaded portion, a middle portion and a second threaded portion. The middle portion comprises a modified threaded portion being configured to mitigate damage to a patient&#39;s nerve root. A first marker is joinable to the shaft proximate the modified threaded portion. The first marker comprises a material being radiographically distinguishable from the shaft in which a placement of the modified threaded portion is observable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims priority to and benefit ofU.S. Utility patent application Ser. No. 13/427,841 filed Mar. 22, 2012,entitled “A Pedicle Screw” which application is a continuation-in-partof and claims priority to and benefit of U.S. Utility patent applicationSer. No. 12/132,476 entitled “Pedicle Screw” filed on Jun. 3, 2008 (nowU.S. Pat. No. 8,740,956) which claims the benefit of provisionalapplication 61/010,669 filed on Jan. 10, 2008.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER LISTING APPENDIX

Not applicable.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor patent disclosure as it appears in the Patent and Trademark Office,patent file or records, but otherwise reserves all copyright rightswhatsoever.

FIELD OF THE INVENTION

One or more embodiments of the invention generally relate to medicaldevices. More particularly, one or more embodiments of the inventionrelate to a modified pedicle screw system.

BACKGROUND OF THE INVENTION

The following background information may present examples of specificaspects of the prior art (e.g., without limitation, approaches, facts,or common wisdom) that, while expected to be helpful to further educatethe reader as to additional aspects of the prior art, is not to beconstrued as limiting the present invention, or any embodiments thereof,to anything stated or implied therein or inferred thereupon. It isbelieved that spine surgery has become a major field in medicine overthe past decades. Because the spine generally provides support andmovement for the body, a problem with the spine (e.g., a back disorder)can disrupt even the simplest activities of life. In general, thousandsof surgical fusions of the spine are performed each year in an attemptto decrease pain and increase function. Stabilization of the spine maybe accomplished in a variety of way including, without limitation, theuse of pedicle screws. A pedicle screw is generally a biocompatiblescrew that is typically inserted into a vertebra at the pedicle, whichis a projection from the body of the vertebra that connects the body ofthe vertebra to the arch of the vertebra. Vertebrae generally have twopedicles.

By way of educational background, an aspect of the prior art generallyuseful to be aware of is that complications from the use of pediclesscrews may occur, which may include, without limitation, loosening ofscrews, breakage of screws, damage to nearby joints, penetration ofmajor blood vessels, and injuries to delicate neurological structuressuch as, but not limited to, nerve roots and the spinal cord. Typically,each level of the spine has an associated nerve root which is locatedjust medial and inferior to the pedicle. The nerve root is typically inintimate contact with the pedicle through which the screw passes. If thepedicle screw violates the inferior or medial wall of the pedicle duringplacement, there may be potential for nerve root injury which may resultin pain and/or dysfunction. Patients with nerves that have been damagedby poorly placed pedicle screws may fail to recover and may suffer fromchronic and disabling pain. The nerve roots may be injured at the timeof surgery, or injury may accumulate over time from the threads of thescrews acting against the nerve roots. Due to the potential to damagethe nerve roots if the threading of a pedicle screw interacts with thenerve root, proper installation of the pedicle screw is generally aconcern in procedures involving pedicle screws.

By way of educational background, another aspect of the prior artgenerally useful to be aware of is that technology has been introducedover the years in an attempt to decrease the risk of nerve damageassociated with placement of pedicle screws. For example, withoutlimitation, one prior art system uses a method of determining the sizeand trajectory of a pedicle screw through 3D imaging. Also, the use ofintraoperative fluoroscopy can reduce the incidence of misplaced screws,as can technology which utilizes computer guidance based on preoperativeCT scanning. Even with these technologies, injury to nerve roots mayresult from the use of pedicle screw fixation.

In view of the foregoing, it is clear that these traditional techniquesare not perfect and leave room for more optimal approaches.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is an illustration of a vertebra in transverse cross section;

FIGS. 2a through 2c illustrate cross sectional views of pedicle screws,in accordance with various embodiments of the present invention;

FIG. 3 is a diagrammatic top view of an exemplary modified pediclescrew, in accordance with an embodiment of the present invention;

FIG. 4 is a diagrammatic side view of an exemplary integrated marker forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention;

FIG. 5 is a diagrammatic side view of an exemplary integrated marker forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention;

FIG. 6 is a cross sectional view of an exemplary internal marker forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention;

FIG. 7 is a cross sectional view of an exemplary internal marker forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention;

FIG. 8 is a cross sectional view of an exemplary removable marker forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention;

FIG. 9 is a side view of an exemplary removable marker for assessingpedicle screw placement, in accordance with an embodiment of the presentinvention; and

FIG. 10 is a side view of an exemplary removable marker in use with adriver for assessing pedicle screw placement, in accordance with anembodiment of the present invention.

Unless otherwise indicated illustrations in the figures are notnecessarily drawn to scale.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Embodiments of the present invention are best understood by reference tothe detailed figures and description set forth herein.

Embodiments of the invention are discussed below with reference to theFigures. However, those skilled in the art will readily appreciate thatthe detailed description given herein with respect to these figures isfor explanatory purposes as the invention extends beyond these limitedembodiments. For example, it should be appreciated that those skilled inthe art will, in light of the teachings of the present invention,recognize a multiplicity of alternate and suitable approaches, dependingupon the needs of the particular application, to implement thefunctionality of any given detail described herein, beyond theparticular implementation choices in the following embodiments describedand shown. That is, there are numerous modifications and variations ofthe invention that are too numerous to be listed but that all fit withinthe scope of the invention. Also, singular words should be read asplural and vice versa and masculine as feminine and vice versa, whereappropriate, and alternative embodiments do not necessarily imply thatthe two are mutually exclusive.

It is to be further understood that the present invention is not limitedto the particular methodology, compounds, materials, manufacturingtechniques, uses, and applications, described herein, as these may vary.It is also to be understood that the terminology used herein is used forthe purpose of describing particular embodiments only, and is notintended to limit the scope of the present invention. It must be notedthat as used herein and in the appended claims, the singular forms “a,”“an,” and “the” include the plural reference unless the context clearlydictates otherwise. Thus, for example, a reference to “an element” is areference to one or more elements and includes equivalents thereof knownto those skilled in the art. Similarly, for another example, a referenceto “a step” or “a means” is a reference to one or more steps or meansand may include sub-steps and subservient means. All conjunctions usedare to be understood in the most inclusive sense possible. Thus, theword “or” should be understood as having the definition of a logical“or” rather than that of a logical “exclusive or” unless the contextclearly necessitates otherwise. Structures described herein are to beunderstood also to refer to functional equivalents of such structures.Language that may be construed to express approximation should be sounderstood unless the context clearly dictates otherwise.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which this invention belongs. Preferred methods,techniques, devices, and materials are described, although any methods,techniques, devices, or materials similar or equivalent to thosedescribed herein may be used in the practice or testing of the presentinvention. Structures described herein are to be understood also torefer to functional equivalents of such structures. The presentinvention will now be described in detail with reference to embodimentsthereof as illustrated in the accompanying drawings.

From reading the present disclosure, other variations and modificationswill be apparent to persons skilled in the art. Such variations andmodifications may involve equivalent and other features which arealready known in the art, and which may be used instead of or inaddition to features already described herein.

Although Claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure of the present invention also includes any novel feature orany novel combination of features disclosed herein either explicitly orimplicitly or any generalization thereof, whether or not it relates tothe same invention as presently claimed in any Claim and whether or notit mitigates any or all of the same technical problems as does thepresent invention.

Features which are described in the context of separate embodiments mayalso be provided in combination in a single embodiment. Conversely,various features which are, for brevity, described in the context of asingle embodiment, may also be provided separately or in any suitablesubcombination. The Applicants hereby give notice that new Claims may beformulated to such features and/or combinations of such features duringthe prosecution of the present application or of any further applicationderived therefrom.

References to “one embodiment,” “an embodiment,” “example embodiment,”“various embodiments,” etc., may indicate that the embodiment(s) of theinvention so described may include a particular feature, structure, orcharacteristic, but not every embodiment necessarily includes theparticular feature, structure, or characteristic. Further, repeated useof the phrase “in one embodiment,” or “in an exemplary embodiment,” donot necessarily refer to the same embodiment, although they may.

As is well known to those skilled in the art many careful considerationsand compromises typically must be made when designing for the optimalmanufacture of a commercial implementation any system, and inparticular, the embodiments of the present invention. A commercialimplementation in accordance with the spirit and teachings of thepresent invention may configured according to the needs of theparticular application, whereby any aspect(s), feature(s), function(s),result(s), component(s), approach(es), or step(s) of the teachingsrelated to any described embodiment of the present invention may besuitably omitted, included, adapted, mixed and matched, or improvedand/or optimized by those skilled in the art, using their average skillsand known techniques, to achieve the desired implementation thataddresses the needs of the particular application.

It is to be understood that any exact measurements/dimensions orparticular construction materials indicated herein are solely providedas examples of suitable configurations and are not intended to belimiting in any way. Depending on the needs of the particularapplication, those skilled in the art will readily recognize, in lightof the following teachings, a multiplicity of suitable alternativeimplementation details.

One or more embodiments of the present invention relate to a pediclescrew for use in spine surgery. In some embodiments this pedicle screwcomprises a modification to the shaft of the pedicle screw involving theremoval of the normal screw threading along a portion of the screw,thereby conceivably making the screw safer by generally reducing thepotential for nerve root injury, as this non-threaded region is lesslikely to cause injury if the nerve passes against it. In some alternateembodiments, the modified portion of the shaft of the screw may bepartially threaded rather than non-threaded. In addition to themodification of the threaded shaft, some embodiments may also comprise asystem to control the rotation of the non-threaded portion of the shaftand the application of a radiographic marker to assess fluoroscopicallythe position of the non-threaded portion of the screw shank withrelation to the anatomic structures of the spine. In order to achievesome of the benefits of the new pedicle screw in some embodiments, it isbelieved that it is advantageous for the non-threaded portion of thescrew to be placed to both the proper depth and the proper rotation withrespect to the associated nerve root with the non-threaded area of thescrew aligned with and facing the nerve root after screw insertion.

FIG. 1 is an illustration of a vertebra in transverse cross section.Referring further to FIG. 1, a typical vertebra 101 is one of the bonescomprising a human spine. The vertebra 100 has several components, avertebral body 105, a vertebral foramen 110, a spinous process 115, apedicle 120, a superior articular process 125, a transverse process 130,and a lamina 135. Two vertebral bodies combine to create the vertebralforemen 110 through which passes a nerve root and a spinal cord 140. Thehuman spine varies widely across the population, and, accordingly, sodoes the pedicle 120. Because the pedicle 120 varies in its anatomy,biocompatible hardware must also be available in various shapes andsizes that is inserted into or otherwise affixed to the pedicle 120, forexample a bone screw.

FIGS. 2a through 2c illustrate cross sectional views of pedicle screws,in accordance with various embodiments of the present invention.Referring further to FIG. 2a , the bone screw (e.g., a pedicle screw200) has a head 205 and a shaft 210. And like any screw, the pediclescrew 200 has various characteristics, for example, without limitation,a length, a major diameter, a minor diameter, a thread pitch, and ataper profile that can all be adjusted given the various pediclepathologies. The shaft 210 for example, without limitation, can have amajor diameter of 6.5 mm, a length of 40 mm, and a thread pitch of 3.0mm, with other measurements contemplated so that the pedicle screw 200performs as intended. The pedicle screw 200 has a first threaded shaftportion 215, a middle shaft portion 220, and a second threaded shaftportion 225. The second threaded shaft portion 225 is contiguous to thehead 205, but alternatively there can be a shank or other portiondisposed between the second threaded shaft portion 225 and the head 205.The middle shaft portion 220 is of an irregular form, which is to say,it does not share at least one of the same characteristics as the firstthreaded shaft portion 215 and the second threaded shaft portion 225.The pedicle screw 200 preferably has a major/minor diameter combinationof cylindrical, so that the middle shaft portion 220 lacks any of thethreading in the first and second threaded shaft portions 215, 225,respectively, and is of the cylindrical minor diameter. Any combinationof cylindrical and tapered diameters are contemplated within thisapplication, for example, without limitation, the minor diameter may betapered and the major diameter cylindrical, in which case, the middleshaft portion 220 would have the tapered minor diameter. Otherembodiments of the presently preferred embodiment are also contemplated,for example, without limitation, those described below.

Referring further to FIGS. 2b and 2c , the middle shaft portion 220 canbe threaded along a portion, for example, without limitation, half ofits cylindrical (or tapered) surface, generally shown at 230. In thisembodiment a marker 235 is placed on the head 205 as a visual indicatorof the location of the non-threaded minor diameter of the middle shaftportion 220. The marker 235 allows for the proper alignment of thepedicle screw 200 such that the threads of the middle shaft portion 220are placed to minimize potential thread contact with the nerve root orspinal cord 140. Referring to FIG. 2c , the middle shaft portion 220 hasa concave feature 240, for example. The concave feature 240 can bethreaded, and is preferably threaded on the non-concave portion, so thatwhen inserted into the pedicle 120, the pedicle screw 200 is alignedsuch that the concave feature 240 minimizes contact with the associatednerve root.

In practice, when pedicle screws are evenly placed with the assistanceor the aid of intraoperative fluoroscopy and/or CT guided imagingtechniques, for example, without limitation, there still exists thepossibility of placement error that can go undetected resulting in nerveroot damage and/or injury. Therefore, it is contemplated that theplacement of the pedicle screw 200 directly addresses when thesedrilling errors are known so that the disclosed pedicle screw 200 willgreatly lessen damage caused by the threads of prior art pedicle screws.

A number of embodiments have been described. It will be understood thatvarious modifications may be made without departing from the spirit andscope of the presently preferred embodiment. For example, withoutlimitation, the biocompatible material contemplated is titanium, butother biocompatible materials are also applicable. The middle shaftportion 220 can be fully threaded but with a smaller thread diameter, orwith blunt edges to protect the nerve. Further, the middle shaft portion220 can be rotated to turn the threads away from the foramen or awayfrom the medial wall of the pedicle. Also, the head 205 can be rotatablefor easy positioning and manipulation.

It is believed that it is generally important for a surgeon performing aprocedure on a spine to be able to verify the placement of a modifiedpedicle screw according to an embodiment of the present invention afterinsertion of the screw. FIG. 3 is a diagrammatic top view of anexemplary modified pedicle screw, in accordance with an embodiment ofthe present invention. In the present embodiment, the head of thepedicle screw comprises a socket 305 into which a driver can only beinserted in one orientation. The non-threaded portion of the pediclescrew shaft is oriented with respect to the shape of socket 305 so thatthe non-threaded portion is aligned with an indicator on the driver whenthe driver is inserted into socket 305. The indicator on the oppositeend of the driver generally enables a surgeon to easily determine therotational orientation of the unthreaded portion of the pedicle screweven after the screw has been inserted into the pedicle. By correctlyorienting the indicator on the driver, the surgeon can align thenon-threaded portion of the screw towards the known position of thenerve root. In addition to this, the screw itself may comprise a markeron the shaft corresponding to the non-threaded portion of the screw, asshown by way of example in FIGS. 2b and 2c . This marker may beradiographically visible to generally enable a surgeon to see the markerand correctly position the non-threaded portion of the screw toward thenerve root when performing a procedure under fluoroscopy.

Some embodiments of the present invention may comprise a radiographicmarker added to a pedicle screw system to allow an operating surgeon toassess the depth and position of a pedicle screw during insertion. Thesystem typically uses a screw with a modified shaft where the threadinghas been removed, as illustrated by way of example in FIGS. 2a through2c . The proper positioning of the screw typically places the unthreadedarea of the screw at the depth of the nerve and facing the nerve afterscrew insertion. The marker generally enables a surgeon to properlyassess the depth and location of the non-threaded portion of the screwand determine its relationship to the location of the nerve root whileperforming a spinal procedure. This may enable the surgeon to minimizepotential interaction between the threads of the pedicle screw and thenerve root. One may expect that the addition of a marker may result inimproved accuracy of screw placement. It is contemplated that a markermay be applied to virtually any type of screw for the purpose ofdetermining the relative depth of placement with regard to anatomicstructures. For example, without limitation, a marker may be made withthe addition of a coating to the screw, as illustrated by way of examplein FIG. 4. In another non-limiting example, as shown by way of examplein FIG. 5, a marker is made of a single band or wire of material, whichis radiographically visible, added to the unthreaded portion of thescrew. Additionally, markers may be placed within the shaft of thescrew, as illustrated by way of example in FIGS. 6 and 7.

FIG. 4 is a diagrammatic side view of an exemplary integrated marker 401for assessing pedicle screw placement, in accordance with an embodimentof the present invention. Marker 401 typically indicates the depth of anon-threaded portion 405 of the screw. In the present embodiment, marker401 is incorporated into the screw by way of an external coating ofadditional material on or in line with the non-threaded portion 405 ofthe screw. This coating is typically made of a material which iscontrasting to the material of the screw under fluoroscopy such as, butnot limited to, various different metals such as gold, tantalum or otherbiocompatible material. This enables marker 401 to generally be seenunder fluoroscopy.

FIG. 5 is a diagrammatic side view of an exemplary integrated marker 501for assessing pedicle screw placement, in accordance with an embodimentof the present invention. In the present embodiment, marker 501 isapplied externally to a screw through the addition of a wire or bandbetween the boundaries of a non-threaded portion 505 of the screw. Insome alternate embodiments two bands or wires may be placed around thescrew at the boundaries of the non-threaded portion of the screw toindicate the top and the bottom of the non-threaded portion of thescrew. In the present embodiment, a small groove is included withoutlimitation in the shaft of the screw in which the wire or band is placedto generally maintain a smooth surface on the screw, particularly atnon-threaded portion 505. In some alternate embodiments, a wire or bandmay be placed around a screw without the use of a groove. In the presentembodiment, marker 501 is made of a material which is contrasting to thematerial of the screw (i.e., radiographically visible).

Those skilled in the art will readily recognize, in light of and inaccordance with the teachings of the present invention, that somealternate embodiments may use a multiplicity of suitable means forcreating a marker on a pedicle screw. For example, without limitation, amarker may be produced by creating a geometrical clue to be seen underthe fluoroscope, such as, but not limited to, a hole drilled in theshaft of the screw or a defect cut in the shaft of the screw. Thismethod generally does not require the attachment of additional materialto the shaft of the screw. In other alternate embodiments, an internalmarker may be used. Internal markers may be placed in a screw bydrilling into the screw and placing a metal that is dissimilar to thematerial of the screw or other contrasting material which provides acontrasting view under radiographic imaging into the hole created by thedrilling. Internal markers may be solid for non-cannulated screws or maybe drilled though for cannulated screws. A cannulated screw comprises achannel in the shaft to create a hollow or partially hollow screw.

FIG. 6 is a cross sectional view of an exemplary internal marker 601 forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention. In the present embodiment, marker 601 is insertedinto the shaft of a screw, which comprises a hole 605 that has beendrilled to enable marker 601 to be inserted into the shaft of the screw.Hole 605 is drilled to a depth corresponding to a non-threaded portion610 of the shaft of the screw so that marker 601 may be aligned withnon-threaded portion 610.

FIG. 7 is a cross sectional view of an exemplary internal marker 701 forassessing pedicle screw placement, in accordance with an embodiment ofthe present invention. In the present embodiment, a screw is fullycannulated and comprises a hole 705 through the entire shaft of thescrew. The diameter of hole 705 near the screw head is sized accordinglyto allow placement of marker 701. Near the tip of the shaft of thescrew, the diameter of hole 705 decreases to generally prevent marker701 from migrating and to generally ensure proper placement of marker701 during use in alignment with a non-threaded portion 710 of thescrew.

The use of a marker such as, but not limited to, those illustrated byway of example in the foregoing embodiments generally enables a user toconfirm after screw placement that the screw has been inserted to theproper depth to place the unthreaded portion of the screw in properrelation to the location of the nerve root. As described above, properscrew rotation is verified by a visual check of the indicator on thedriver or on the screw. The ability to control both the depth androtational orientation of the non-threaded portion of the modified screwgenerally enables a surgeon to minimize the risk of nerve root injuryduring screw placement. In addition to improving the accuracy of theplacement of the unthreaded portion of the pedicle screw with regard tothe nerve root, the addition of a marker may also enable the unthreadedportion of the screw to be made smaller because of this improvedaccuracy. The use of a smaller unthreaded portion enables the screw tohave a greater portion of the shaft covered with threading, which mayresult in a screw with greater purchase and pull out strength as well asimproved safety with regard to potential nerve root injury.

FIG. 8 is a cross sectional view of an exemplary removable marker 801for assessing pedicle screw placement, in accordance with an embodimentof the present invention. In the present embodiment, marker 801 isdesigned to be attached to the end of a wire 805. Wire 805 enablesmarker 801 to be placed inside a hole 810 in a screw before or after theinsertion of the screw into a patient's pedicle. Wire 805 also enablesmarker 801 to be removed from hole 810 after verification of the depthof the screw. The length of wire 805 can be also used to ensure that themarker 801 is inserted to the proper depth inside the screwcorresponding to the non threaded portion of the screw. By cutting thewire to a measured length or by applying a marker to the opposite end ofthe wire, (the end not passing into the screw), the depth of theradiographic marker's insertion into the pedicle screw can be controlledto ensure the radiographic marker is properly situated inside the screw.The screw may be fully and equally cannulated, or cannulated just to thedepth of an unthreaded portion 815 of the screw at a diameter into whichmarker 801 may be inserted. The remaining portion of the shaft of thescrew could be cannulated in a smaller diameter producing a step toprevent the marker from advancing too far into the screw. In somealternate embodiments, the remaining portion of the shaft may not becannulated. In the present embodiment, the length of marker 801 is equalto the length of unthreaded portion 815 of the screw. Fluoroscopy isused for verification of the placement of unthreaded portion 815.

FIG. 9 is a side view of an exemplary removable marker for assessingpedicle screw placement, in accordance with an embodiment of the presentinvention. In the present embodiment, marker 901 is designed to beattached to the end of a wire 905. Wire 905 enables marker 901 to beplaced inside a hole 810, shown in FIG. 8, in a screw before or afterthe insertion of the screw into a patient's pedicle. Wire 905 alsoenables marker 901 to be removed from hole 810 after verification of thedepth of the screw. The length of wire 905 can be also used to ensurethat the marker 901 is inserted to the proper depth inside the screwcorresponding to the non threaded portion of the screw. By applying asecond marker 920 to the opposite end of the wire, the depth of theradiographic marker 901 insertion into the pedicle screw may becontrolled. Additionally a stop 925 may attached the wire 905 for usewith a driver, as shown by way of example in FIG. 10, to ensure that themarker 901 is inserted to the proper depth inside the screwcorresponding to the non threaded portion of the screw.

FIG. 10 is a side view of an exemplary removable marker in use with adriver for assessing pedicle screw placement, in accordance with anembodiment of the present invention. In the present embodiment, intypical use, wire 1005 with markers 1001 and 1020 and stop 1025 areinserted into driver 1030. Driver 1030 may be used to drive the pediclescrew into the patient's bone. Stop 1025 is positioned on wire 1005 suchthat, when wire 1005 is placed into driver 1030 and stop 1025 contactsthe top of the driver, marker 1001 protrudes from the driver thedistance required to properly place marker 1001 in the desired positionin the cannulated screw when driver 1030 engages the pedicle screw.

All the features disclosed in this specification, including anyaccompanying abstract and drawings, may be replaced by alternativefeatures serving the same, equivalent or similar purpose, unlessexpressly stated otherwise. Thus, unless expressly stated otherwise,each feature disclosed is one example only of a generic series ofequivalent or similar features.

Having fully described at least one embodiment of the present invention,other equivalent or alternative methods of providing a pedicle screwsystem according to the present invention will be apparent to thoseskilled in the art. The invention has been described above by way ofillustration, and the specific embodiments disclosed are not intended tolimit the invention to the particular forms disclosed. For example, theparticular implementation of the depth marker may vary depending uponthe particular type of screw used. The depth markers on non-cannulatedscrews described in the foregoing were directed to integratedimplementations; however, similar techniques are to provide removabledepth markers on non-cannulated screws. For example, without limitation,a removable marker with threading may be threaded onto a non-cannulatedscrew. Implementations of the present invention in which removable depthmarkers are included without limitation on non-cannulated screws arecontemplated as within the scope of the present invention. The inventionis thus to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the following claims.

Claim elements and steps herein may have been numbered and/or letteredsolely as an aid in readability and understanding. Any such numberingand lettering in itself is not intended to and should not be taken toindicate the ordering of elements and/or steps in the claims.

What is claimed is:
 1. A method for installing a pedicle screw in apatient comprising: a) providing a pedicle screw having a head and ashaft with threads, said shaft comprising a modified portion configuredto mitigate damage to the patient's nerve root and a portion of theshaft is threaded substantially its entire length, said screw having aremovable marker within a channel in said shaft proximate to saidmodified portion, said marker being radiographically distinguishablefrom said shaft and capable of positioning within and movinglongitudinally within and ultimately removable from said shaft in whichplacement of said modified portion is observable with respect to saidmodified portion; b) installing the screw in a pedicle of the patient;c) radiographically observing the placement of said marker with respectto the modified portion of the pedicle screw and the pedicle nerve rootof the patient; and d) orienting placement of said screw so as not toirritate the pedicle nerve root of the patient.
 2. The pedicle screw ofclaim 1 wherein the channel extends from said head through at least themodified portion of said shaft.
 3. The method of claim 2 wherein thechannel further extends to an end of said shaft in which said marker isrestricted from entering.
 4. The method of claim 1 in which the markeris disposed on a wire, said wire being inserted into the channel of thepedicle screw to a position wherein the marker corresponds to thepedicle nerve root of the patient and allowing for radiographicallydetermining the location of said modified portion of the screw withrespect to the patient's nerve root.
 5. The method of claim 4 in whichthe marker is positioned within said screw such that the markercorresponds to the presumed location of the patient's pedicle nerveroot.
 6. The method of claim 4 in which the wire and the marker areremoved from the screw after placement of the screw.
 7. The method ofclaim 1 in which the modified portion of the shaft is at least in partunthreaded.
 8. The method of claim 7 in which the modified portion ofthe shaft is concave.
 9. The method of claim 1 wherein the headcomprises a socket that engages a driver for driving said pedicle screwinto a pedicle, said socket being operable for indicating a rotationalalignment of said modified portion of the screw.
 10. The method of claim1 wherein said modified portion is a middle part of the threaded portionof the screw.
 11. A method for installing a pedicle screw in a patientcomprising: a) providing a pedicle screw having a head and a shaft withthreads, said shaft comprising a middle unthreaded portion on a portionof said shaft, said screw having a marker joinable to said shaftproximate to said middle portion, said marker being disposed on a wirewithin an internal channel in said screw and said marker beingradiographically distinguishable from and capable of movinglongitudinally within and ultimately removable from said shaft, in whichplacement of said middle unthreaded portion is observable with respectto said unthreaded portion and the location of the patient's nerve root,said wire bearing a second marker opposite a position of the firstmarker wherein the second marker is used to control a depth the firstmarker is inserted within the internal channel to correspond with thelocation of the middle unthreaded portion of the shaft; b) installingthe screw in a pedicle of the patient; c) radiographically observing theplacement of said markers with respect to the unthreaded portion of thepedicle screw and the pedicle nerve root of the patient; and d)orienting placement of said screw so as not to irritate the pediclenerve of the patient.
 12. The method of claim 11 wherein the wire andmarkers are removed from the screw after placement of the screw, andfurther wherein a diameter of the channel decreases near a tip of thescrew to prevent the markers from migrating.
 13. The method of claim 11wherein said head comprises a socket that engages a driver for drivingsaid pedicle screw into a pedicle, said socket being operable forindicating a rotational alignment of said middle unthreaded portion. 14.The method of claim 11 wherein the pedicle screw is fully cannulated.